In the present quantum optics and laser physics study, the non-linear interaction\nof electromagnetic fields with atomic, molecular and biomolecular media is analyzed.\nParticular emphasis is given to coherent phenomena, while propagation and dispersion\neffects are also extensively investigated. The fields involved vary from ultra short\npulses to continuous waves; while their energies range from the very strong that are\naddressed classically, to the very weak which are described quantum mechanically.\nApplications and problems addressed span a wide range. A scheme for a real time\ndetector of chemical and biological hazards, like anthrax spores, is presented; in it,\na strong spectroscopic signature is obtained from complex molecules by using ultrashort,\nfemtosecond, laser pulses and inducing vibrational coherence on them. Furthermore,\na way of reversing the phase matching condition in coherent spectroscopy,\nbased on dispersion, is developed; which allows for the use of such spectroscopic methods\nin remote detection. More fundamental questions addressed include a resolution\nof the centennial old paradox of Maxwell's demon via quantum thermodynamics, and\nthe role of atomic coherence in enhancing the efficiency of a heat engine as well as\nin obtaining lasing without population inversion. Additionally, a quantum storage\nscheme is presented, in which the information contained in an optical pulse is stored\nand restored via photon echoes.
In the present quantum optics and laser physics study, the non-linear interaction\nof electromagnetic fields with atomic, molecular and biomolecular media is analyzed.\nParticular emphasis is given to coherent phenomena, while propagation and dispersion\neffects are also extensively investigated. The fields involved vary from ultra short\npulses to continuous waves; while their energies range from the very strong that are\naddressed classically, to the very weak which are described quantum mechanically.\nApplications and problems addressed span a wide range. A scheme for a real time\ndetector of chemical and biological hazards, like anthrax spores, is presented; in it,\na strong spectroscopic signature is obtained from complex molecules by using ultrashort,\nfemtosecond, laser pulses and inducing vibrational coherence on them. Furthermore,\na way of reversing the phase matching condition in coherent spectroscopy,\nbased on dispersion, is developed; which allows for the use of such spectroscopic methods\nin remote detection. More fundamental questions addressed include a resolution\nof the centennial old paradox of Maxwell's demon via quantum thermodynamics, and\nthe role of atomic coherence in enhancing the efficiency of a heat engine as well as\nin obtaining lasing without population inversion. Additionally, a quantum storage\nscheme is presented, in which the information contained in an optical pulse is stored\nand restored via photon echoes.
It is well known that the optical properties of multi-level atomic and molecular system can be controlled and manipulated efficiently using quantum coherence and interference, which has led to many new effects in quantum optics for e.g. lasing action without population inversion, ultraslow light, high resolution nonlinear spectroscopy etc. Recent experimental and theoretical studies have also provided support for the hypothesis that biological systems uses quantum coherence. Nearly perfect excitation energy transfer in photosynthesis is an excellent example of this.\n\nIn this dissertation we studied quantum coherence and interference effects in the transient and the continuous-wave regimes. This study led to (i) the first experimental demonstration of carrier-envelope phase effects on bound-bound atomic excitation in multi-cycle regime (~15 cycles), (ii) a unique possibility for standoff detection of trace gases using their rotational and vibrational spectroscopic signals and from herein called Coherent Raman Umklappscattering, (iii) several possibilities for frequency up-conversion and generation of short-wavelength radiation using quantum coherence (iv) the measurement of spontaneous emission noise intensity in Yoked-superfluorescence scheme.\n\nApplications of the obtained results are development of XUV (X-Ray) lasers, con- trolled superfluorescent (superradiant) emission, carrier-envelope phase effects, coherent Raman scattering in the backward direction, enhancement of efficiency for generating radiation in XUV and X-Ray regime using quantum coherence with and without population inversion and to extend XUV and X-Ray lasing to ~4.023 nm in Helium-like carbon.
Coherent preparation by laser light of quantum states of atoms and molecules can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to electromagnetically induced transparency and related effects, which have placed gas-phase systems at the center of recent advances in the development of media with radically new optical properties. This article reviews these advances and the new possibilities they offer for nonlinear optics and quantum information science. As a basis for the theory of electromagnetically induced transparency the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser. They then discuss pulse propagation and the adiabatic evolution of field-coupled states and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments. The extension of these concepts to very weak optical fields in the few-photon limit is then examined. The review concludes with a discussion of future prospects and potential new applications.
Coherent atomic states prepared by laser field can have quantum interference\nbetween the different transition amplitudes. Therefore, the medium susceptibility\nand optical response can be engineered, leading to many interesting phenomena, such\nas coherent population trapping (CPT), electromagnetically induced transparency\n(EIT), and lasing without inversion (LWI).\nWe studied the coherence effects in various prototype atomic systems, and found\nmany interesting applications. We solved the slow light bandwidth problem by decomposing\nthe pulse and matching each frequency to its EIT window using a magnetic\nfield gradient. We also considered the probe field deflection induced by the driving\nfield distribution in EIT, and showed that even a broadband pulse can be deflected\nwithout serious spreading. In the fast light area, we examined the effects of noise and\nparameter deviations in a bichromatic Raman type white light cavity. Taking advantage\nof the adjustable absorption of EIT, we showed that EIT in a laser cavity can\nhave either first-order or second-order phase transitions. Last but not least, we show\nthat the adiabatic population transfer can be used to reverse the weak measurement\nof an arbitrary field with finite photon number.
During the last half century, quantum coherence has been of great interest due to its own right and also due to its broad range of applications in many areas of physics. The reason for that is the technological progress made last century, specially, the invention of coherent light sources and their commercialization. Indeed, coherent laser sources allow us to coherently excite atoms and molecules, as a consequence, to study variety of coherent and collective phenomena in atomic physics, for instance, coherent optical spectroscopy, superradiance, superflourescence, lasing without inversion and so forth. Interestingly, recent studies in biological systems also seem to exhibit coherent processes, in particular, photosynthetic transport and avian compass.\n\nIn this dissertation, we present some of the theory and applications of the quantum coherence. This study considers (i) application of quantum coherence to enhance output signals of coherent anti-Stokes Raman spectroscopy of optically active media (chiral molecules), (ii) a way to find general formulas of single- and double-excited subradiant Dicke states using symmetry group theory, (iii) an impact of Fano-Agarwal coupling and other virtual processes arising from non-rotating wave approximation on the decay of super and subradiant timed Dicke states, and finally (iv) quantum coherence and collective phenomena of relativistically and uniformly accelerating atoms.\n\nApplications of the results presented in the dissertation may be a new method for resolving chirality of molecules using coherent anti-Stokes Raman spectroscopy - Raman optical activity, and a sidewise excitation method for single- and double-excited subradiant states. The obtained results also advance our theoretical understanding of quantum coherence specially theory of super and subradiance.
When matter is exposed to strong fields, electrons are ionized and a number of processes such as high harmonic generation (HHG), above threshold ionization (ATI), non-sequential ionization happen. These processes are usually investigated semiclassically, i.e. matter is treated by quantum mechanics, and radiation is treated classically. In particular HHG which is the generation of ultrashort coherent extreme ultraviolet (XUV) pulses, has enabled a wealth of novel ultrashort spectroscopic methods in atomic, molecular, and condensed matter physics. Further, ionization has applications in micro-machining. Strong field physics continues to have numerous open questions. As an illustration, the mechanisms underlying dominant HHG pathways in solids remain insufficiently understood. It is not clear which mechanism dominates HHG in various materials. Possible pathways are the interband and intraband contributions. Furthermore, many of these processes in strong field physics have been described by single active electron (SAE) approximation. This approach relies on the assumption that the interaction between a single electron and the intense laser field dominates all other interactions. However, this is clearly not the case especially in solids where interactions with the lattice and other electrons can be important. In addition, quantum optical aspects of strong field physics have generated increasing interest, yet they remain partially explored. This chapter involves treating electromagnetic fields using the formalism of second quantization. Quantum optical properties, such as squeezing, entanglement and the negativity of the Wigner function, are of fundamental importance for the field of quantum information and quantum computation. The central theme of my thesis is the development of quantum optical and statistical theoretical frameworks for describing intense laser field processes such as ionization and HHG in atomic and molecular gases and in solids. The second chapter focuses on gaining a detailed understanding of the mathematical steps involved in the Keldysh theory of ionization to establish a solid theoretical foundation. Through this analysis we identified an additional factor of two compared to Keldysh’s original derivation of atomic ionization rates. The third chapter addresses the inadequately understood mechanisms that govern dominant high harmonic generation (HHG) pathways in solids. One approach to clarify these mechanisms involves introducing real (resonant) and virtual processes. We developed the strong field adiabatic following (SFAF) formalism which is based on Dyson expansion using the von-Neumann equation of density matrix. Using SFAF a diagnostic method is obtained to separate virtual and resonant channels. Through this separation, and by comparing with experimental results, we identified the need to incorporate many-body effects. The fourth chapter explores the fact that a solid is a complex many body system in which the SAE approximation is very crude. The electron interacts with holes, other electrons, collective excitations such as plasmons, and phonons. Our work is based on the idea that all theses effects can be treated as a quantum statistical heat bath of bosonic harmonic oscillators. We apply this to our SFAF formalism. In the ionization case, this work has settled a long standing issue which is the fact that simple phenomenological approaches such as the relaxation time approximation 𝑇2 result in nonphysical enhancement of ionization. In chapter five, we have investigated ways to transfer quantum optical properties on the otherwise classical high harmonic radiation. The goal is to use HHG to scale quantum sources to smaller wavelengths. Quantum properties can be imprinted by perturbing HHG with a quantum field, such as bright squeezed vacuum (BSV). In this chapter, the theory of quantum sideband high harmonic generation (QSHHG) in atoms and solids is derived to find ways by which to transfer quantum properties from the perturbative BSV to the harmonic sideband. The theoretical framework is a quantum generalization of the semi-classical Lewenstein model of HHG. It gives closed-form solutions for the HHG and QSHHG wavefunctions. Knowing the wavefunction, we can identify the quantum properties of QSHHG. The additional photons absorbed and emitted from the quantum perturbation, here BSV, create entanglement between individual harmonic sidebands and between the harmonic sidebands and the BSV. We show how this entanglement can be used to create a variety of non-classical states commonly used in quantum information science, such as high-purity single-photon states, Schrödinger cat states, and photon-added squeezed vacuum states. Some of these non-Gaussian states with negative Wigner functions have been shown to provide a quantum computational advantage over their Gaussian counterparts. Additionally, they play a significant role in quantum metrology, enhancing precision measurements beyond classical limits. This chapter has opened a path to quantum engineering of HHG.
Abstract This book bridges the gap between introductory quantum mechanics and the research front of modern optics and scientific fields that make use of light. While suitable as a reference for the specialist in quantum optics, it also targets non-specialists from other disciplines who need to understand light and its uses in research. It introduces a single analytic tool, the density matrix, to analyze complex optical phenomena encountered in traditional as well as cross-disciplinary research. It moves swiftly in a tight sequence from elementary to sophisticated topics in quantum optics, including optical tweezers, laser cooling, coherent population transfer, optical magnetism, electromagnetically induced transparency, squeezed light, and cavity quantum electrodynamics. A systematic approach starts with the simplest systems—stationary two-level atoms—then introduces atomic motion, adds more energy levels, and moves on to discuss first-, second-, and third-order coherence effects that are the basis for analyzing new optical phenomena in incompletely characterized systems. Unconventional examples and original problems are used in exploring a mathematical methodology which can tackle virtually any new problem involving light. The steady progression from "simple" to "elaborate" makes the book accessible not only to students from traditional subject areas that make use of light, but also to researchers such as biophysicists using mechanical effects of light; photochemists developing coherent control for rare species detection; biomedical engineers imaging through scattering media; electromechanical engineers working on molecular design of materials for electronics and space; electrical and computer engineers developing schemes for quantum computation, cryptography, frequency references, and the like.